Non-aqueous electrolyte solution batteries, such as lithium secondary batteries, are being put to practical use in a wide range of application fields from a so-called consumer-oriented power source for a cellular phone, a notebook computer, or the like, to an on-vehicle power source for driving an automobile. However, recent years have been seen increasing demands for higher performance on the non-aqueous electrolyte solution batteries: it is demanded to achieve excellent cycle characteristics in addition to large capacity and a high level of high-temperature-storage characteristics.
Accordingly, in order to obtain a non-aqueous electrolyte solution battery with a higher capacity, current designing methods are commonly intended to cram the largest possible amount of active material into a limited battery volume, such as the method in which pressure is applied to the active material layer of the electrode so as to increase its density and reduce the space remaining in the electrode. However, if the space within the battery is diminished, there arises a problem that even when a small amount of gas is generated due to decomposition of the electrolyte solution, the internal pressure of the battery remarkably increases.
Also, when a non-aqueous electrolyte solution battery is used as a backup power source in case of a power failure or a power source of a portable device, in order to compensate for self discharging of the battery, the battery is continuously supplied with a weak current and is constantly put in a state of charging. In such a state of continuous charging, the active materials in the electrodes keep exhibiting a high level of activity while, due to heat generated in the device, the capacity of the battery may acceleratingly decrease or the electrolyte solution may decompose and tend to bring about the generation of gas. Especially in a type of battery that detects an abnormal increase in its internal pressure due to abnormalities such as overcharging and activates a safety valve, generation of a large quantity of gas may also activate the safety valve. On the other hand, in a battery having no safety valve, the pressure of the generated gas may dilate the battery and disable the battery per se.
In order to obtain a non-aqueous electrolyte solution battery that satisfy various properties required for non-aqueous electrolyte solution batteries, including the prevention of gas generation as mentioned above, various compounds are being examined in search of an additive to a non-aqueous electrolyte solution.
For example, Patent Document 1 discloses that when a non-aqueous electrolyte solution using an asymmetric chain carbonic ester compound is used as a non-aqueous solvent while a cyclic carbonic ester compound having double bonds is added thereto, the cyclic carbonic ester compound having double bonds preferentially reacts with a negative electrode to form a coating of good quality over the negative electrode surface, so that the forming of a non-conductive coating over the negative electrode surface caused by the asymmetric chain carbonic ester compound is inhibited, and that the resultant secondary battery shows improvements in its storage characteristics and cycle characteristics.
Patent Document 2 discloses that by adding a carbonic ester compound having ether linkages to a non-aqueous electrolyte solution, the compound covers active spots on the positive electrode surface, oxidative decomposition of a non-aqueous solvent contained in the electrolyte solution can be inhibited, so that the resultant secondary battery shows improvement in its storage stability at high temperature and high voltage.
Patent Document 3 discloses that adding benzene sulfonyl fluoride or p-toluene sulfonyl fluoride to a non-aqueous electrolyte solution improves discharging characteristics at low temperature, so that a battery having excellent cycle characteristics can be obtained.
Patent Document 4 discloses that when an electrolyte solution includes an ether compound having a specific structure containing fluorine atoms, runaway reaction due to overheating does not occur, so that the electrolyte solution shows improved safety.
Patent Document 5 discloses that when one or more of aromatic compounds, esters, carbonates and monoethers having a specific structure including fluorines are contained in an electrolyte solution, generation of hydrogen gas due to decomposition of the electrolyte solution is inhibited at an interface between the positive electrode and the separator, so that swelling of the battery can be inhibited even in high temperature surrounding.
Patent Document 6 discloses that when a cyclic ether compound is added to a non-aqueous electrolyte solution using a mixture of a cyclic carbonic ester and a chain carbonic ester as a non-aqueous solvent, the resultant battery has large capacity and is excellent in cycle characteristics.
Patent Document 7 reports that when a compound monomer or polymer whose molecule contains an amide group is used for forming a coating of a negative electrode, the heat-resistance stability of the negative-electrode coating can be improved.
[Patent Document 1] Japanese Patent Laid-Open Application No. Hei 11-185806
[Patent Document 2] Japanese Patent Laid-Open Application No. 2002-237328
[Patent Document 3] Japanese Patent Laid-Open Application No. 2002-359001
[Patent Document 4] The pamphlet of International Publication No. 00/16427
[Patent Document 5] Japanese Patent Laid-Open Application No. 2002-343424
[Patent Document 6] Japanese Patent Laid-Open Application No. Hei 10-116631
[Patent Document 7] Japanese Patent Laid-Open Application No. 2003-31260